Operational needs require that the air and/or gas inside an engine's crankcase is removed. This ensures that pressure does not build up due to blowby gas past the rings and pistons of the engine, and that fuel and water do not accumulate in the crankcase. Worldwide there are regulations that require the crankcase gasses to be passed through the combustion chamber, to minimize the release of harmful emissions. One method for doing this is to connect the crankcase to the intake manifold, downstream of the throttle for naturally aspirated engines, and upstream of the compressor for boosted engines as shown in U.S. Pat. No. 8,695,339.
This flow constitutes a potential shift to the engine's calibration in that this gas flow may vary due to the pressure drop between the crankcase and the intake manifold. Furthermore, the mixture of oil vapor, fuel vapor, products of combustion, and water that exits the crankcase can form deposits on any valving used to control the flow to a fixed amount, which may be undesirable.
A need exists for improved restrictors in such systems to ensure that flow is generally or even substantially constant, while avoiding the problems with the valves. A simple solution that minimizes the mass and volume flow variation of the fluid through the restrictor in response to variations in manifold pressure is needed.